Chromium plating process



No Drawing.

Patented Oct. 11, 1932 1 UNITED STATES WARREN NOBLE AND CARL J. WELCOME, DETROIT, MICHIGAN, ASSIGNORS TO ELEC- TBOMASTER, INC 01' DETROIT, MICHIGAN, A CORPORATION OE MICHIGAN OHBOHIUI PLATING PROCESS Our invention relates to an improved method for chromium plating metallic surfaces.

Chromium plating has replaced nickel for many purposes due to its superior ap arance and durability. However, its a vantages have not been realized to the fullest extent by heretofore known methods of chromium plating. The present invention provides a plating bath for use in chromium plating which results in a superiorproduct, particuiarly from the standpoint of its resistance to corrosion. Our improved process also permits the use of a much weaker solution of chromic acid than has before been known, and this in turn makes possible the use of a higher current density.

It is, accordingly, an object of this invention to provide an improved method for producing a chromium plate of superlor appearance which will withstand corrosion better than those now in use.

It is a further object of this invention to provide a. chromium plating bath which can be made more diluted than those now in use and still roduce a satisfactory product.

It is a urther object of this invention to provide a chromium plating bath or electrolyte which will produce a plate of superior quality.

In ordinary chromium plating operation,

the electrolyte used ,may contain, for ex-' ample, 250 grams of chromic oxide (CO per litre of solution and 2.5 grams of sulfuric acid (H SO per litre of solution. The anode is usua ly lead while the cathode consists of the object to be plated, which has been very carefully cleaned. The anode and cathode are then connected to a suitable source of current in the usual way.

Our improvement lies in the composition of the electrolyte. Instead of the simple solution of chromic. oxide containing the required proportion of sulphate ions described above, we use a solution containing in addition to chromic acid and sulphate ions, a small amount of a salt of lanthanum or neodymium. We prefer to use the oxalates of these metals.

We offer the following example to illus- Application. filed larch 16, 1931. Serial No. 523,185.

trate our invention, but we do not propose to limit ourselves to the exact procedure therein described.

The article to be plated is first polished and buffed until the desired degree of smoothness has been obtained over the portions which it is desired to plate. It is then lowing composition:

Grams per litre Ghromic oxide 50 Sulfuric acid 0.5 Lanthanum oxalate 0.005

These proportions may vary within a wide range. The chrome oxide may vary from 45 to 7 0 grams per litre, and the acid from .40 to .70 grams per litre, and the lanthanum oxalate may vary within proportional limits.

The anodes are of lead as previously described. The bath should be kept between the temperatures of 125 and 150 F. The current density is kept at about 150 amperes per square foot of cathode surface for about 15 minutes. At the end of which time the plate will have a thickness of .0002 inch which is suitable for most purposes. Lastly, the arizicle is rinsed to remove the adhering electroyte.

The chromium plate produced by this process is much superior to that heretofore available due to its resistance to corrosion, as can be demonstrated by the salt spray corrosion test. Our product shows up remarkably Well under this test as compared with other chromium plates now in use.

It will be seen that we have devised an improved chromium plating bath which is much less concentrated than anV now in use, and

which will permit the use of a higher current density thanthe baths previously known and. also that we have devised'a plating bath which produces a superior product.

It is evident that various departures may be made from the procedure described with out departing from the spirit of our invention and we, therefore, do not propose limit 5 ing the patent granted hereon otherwise than necessitated by the prior art.

W claim asour invention:

1. An electrolyte for use in chromium plating which contains small quantities of a lanthanum salt.

2. An electrolyte for use in chromium plating which contains small quantities of a neodymium salt.

3. An electrolyte for use in chromium plat-.

ing which contains approximately 0.005

' gram of lanthanum oxalate per litre.

4. An electrolyte for use in chromium plating which contains approximately 0.005 gram of neodymium oxalate per litre.

9/ 5. An electrolyte for use in chromium plating consisting of a solution containing substantially 50 grams per litre of chromium oxide, .5 gram per litreof sulfuric acid, and 0.005 gram per litre of lanthanum oxalate.

6. An electrolyte for use in chromium plat- .in which consists of a solution containing su stantially 50 grams per litre of chromic oxide, .5 gram per litre of sulfuric acid, and

0.005 gramper litre of neodynium oxalate.

39 I 7. A process of chromium plating which comprises passing a plating current through an acid bath, containing chromic oxide, sulfate ions and a small quantity of a salt of lanthanum.

8. A process for chromium plating which comprises passing a plating current through an acid bath containing chromic oxide, sulfate ions and a small quantity of a salt of neodymium.

9. Aprocess for chromium plating which comprises passing a plating current through a bath containingsubstantially grams per litre of chromic oxide, .5 gram per litre of sulfuric acid and .005 gram per litre of lanthanum oxalate.

10. A process for chromium plating which comprises passing a plating current through a bath containing substantially 50 grams per litre of chnomic oxide, .5- gram per litre of 50 sulfuric acid and .005 gram per litre of neodymium oxalate.

11. An electrolyte for use in chromium plating which contains small quantities of salts of a metal from a group consisting of lanthanum and neodymium.

. 12. An electrolyte for use in chromium plating which contains small quantities of oxalates ofa metal from a group consistingof lanthanum and neodymium.

In testimony whereof, we have hereunto subscribed our names at Detroit, Mich., County of Wayne.

WARREN NOBLE. Y CARL J. WELCOME. 

